How much is the Word and PowerPoint for MacBook Air???

Apple iWork Pages, Keynote, and Numbers are free from Apple, and can read and write many Office documents.

LibreOffice and OpenOffice are free and open-source packages, and can also read and write many Office documents.

Or go ask Microsoft about their products, pricing, and any offers they might have available.

See: https://products.office.com/en-ca/compare-all-microsoft-office-products?&activetab=tab:primaryr1

It's the same price as it is for any Mac. Check the Microsoft Office site.

https://www.office.com/